/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlineIdentityInterface.h
Converts from a PlatformUserId used by application code to a local user num used by the online system
The corresponding user number of INDEX_NONE if invalid
virtual int32 GetLocalUserNumFromPlatformUserId ( [FPlatformUserId](API\Runtime\Core\Misc\FPlatformUserId) PlatformUserId ) const